The present invention relates to a control circuit for a combination voltage and current source that is current limited in the voltage source mode and voltage limited in the current source mode.
In various applications, it is often required to have a voltage source operating at given voltage unless certain current limits are exceeded. Such voltage sources, for example, allow the testing of various circuits and components while minimizing the chance of damage to either the item under test or the voltage source.
Similarly, it is often required to have a current source operating at a given current unless certain voltage limits are exceeded.
Rather than having both a voltage source and a current source, it is useful to have one apparatus that can act as a current-limited voltage source or a voltage-limited current source.
However, such an apparatus must be able to control all four possible quadrants of operation. It must be able to handle positive or negative voltage in combination with positive or negative current. Voltage and current of opposite polarity can occur if the device connected to the apparatus can also act as a source of current or voltage. This may be no more than, for example, a capacitive load connected to the apparatus when the value of the voltage source is lowered, the capacitor seeking to discharge its then excess charge through the apparatus.
In addition, in many applications it is desirable to utilize a zero voltage source or a zero current source. This can effectively collapse the four quadrants into to what can easily become an unstable configuration. Near zero, the control circuitry may be unable to determine the correct polarity of signals for proper control.